Hydrogen is stored conventionally as a gas or a liquid. Hydrogen storage as a gas is typically in large, bulky steel cylinders at very high pressures (e.g. 2,000 psi). Hydrogen storage as a liquid is typically in insulated containers at very low temperatures. Energy must be used to liquify the hydrogen. Hence, cryogenic hydrogen production and storage is highly inefficient.
Within recent years, considerable attention has been focused on the storage of hydrogen as a metallic compound, or hydride, of various substances. Metal hydrides can store large amounts of hydrogen at low pressures in relatively small volumes. This low pressure storage of hydrogen is relatively safe and allows the construction of hydrogen containers having forms significantly different than those storing gaseous hydrogen. Hydridable metals are charged with hydrogen by introducing pressurized gaseous hydrogen into valved containers. The hydrogen gas reacts exothermically with the metal to form the metal hydride compound. Conversely, the hydrogen is released from the metal hydride by opening the valve of the container to permit decomposition of the compound in an endothermic reaction.
The use of solid hydridable materials to store hydrogen is disclosed in numerous patents, such as U.S. Pat. Nos. 3,508,514, 3,516,263 and 4,036,944, each incorporated herein by reference. These solid hydridable materials are characterized by an interrelation of temperature, pressure and hydrogen content, such that, at any given temperature, the hydrogen content of the hydridable material is determined by the partial pressure of the hydrogen in contact with that material. Generally, as temperature rises it takes a greater partial pressure of hydrogen to maintain a given concentration of hydrogen in the hydridable material. The converse is also true as temperature decreases.
The reversible storage of hydrogen in the form of an intermetallic hydride has several advantages over conventional gaseous and liquid hydrogen storage. The use of metal hydrides offer pronounced volumetric advantages over compressed gas, along with much lower required pressure, a safety advantage. In addition, the use of metal hydrides provides excellent insurance that the hydrogen released from the containers is of very high purity.
Metal hydride storage units have many uses and applications in a variety of industrial and laboratory environments. The diversity of applications requires a storage system that can provide the end-user with a reliable source of hydrogen at a variety of capacities. A modular metal hydride hydrogen storage system is needed that can be easily and safely modified by an end-user to provide reliable hydrogen storage for a variety of applications.
U.S. Pat. No. 4,489,564 to Haussler is directed toward a metal hydride storage device for hydrogen but fails to show how several modules may be directly coupled to provide a modular metal hydride hydrogen storage system. U.S. Pat. No. 1,835,887 to Mackey describes a series of interconnected gas expansion chambers that increase in size from inlet to outlet. Mackey, however, contains no teaching or suggestion of metal hydride hydrogen storage modules.
Commonly assigned U.S. Pat. No. 5,697,221 as well as commonly assigned U.S. patent application No. 08/623,497 disclose modular metal hydride storage systems. The disclosures of U.S. Pat. No. 5,697,221 and U.S. patent application No. 08/623,497 are herein incorporated by reference. The present patent application describes a modular metal hydride storage system that includes a system of valved ports that provide the end-user with a very simple and reliable means of coupling and decoupling individual storage modules to create a hydrogen storage system of desired capacity.